The field of the present invention relates to data reading systems. In particular, a method and apparatus are described herein for creating an optical code scanner with a wide range of reading distances.
Longer range scanners have been proposed of a variety configurations. In U.S. Pat. No. 5,869,827 multiple beam sources and distance sensing mechanisms are employed to provide an extended focus range. In U.S. Pat. No. 5,641,958 as employed in the PSC SP400LR scanner, an LCD diffractive control module changes the waist location of the scanning beam. In U.S. Pat. No. 4,560,862 the facets of a polygon mirror are provided with different curvatures such that the scan lines produced by the different facets are focused at varying distances.
The present invention is directed to a system for and a method of generating scan lines having different beam characteristics. In a preferred system, one or more beam characteristics, such as focal distance, scan angle, beam power, or polarization of the scan beam are automatically adjusted as between consecutive scans of the scanning mechanism. For example, the beam may be focused at different distances depending upon the scan line. In a preferred embodiment, the system comprises a light source generating a reading beam, a suitable scanning mechanism such as a polygon mirror having a plurality of mirror facets, and a beam correction plate in the beam path mounted to the facet wheel and rotating therewith. The reading beam passes through the correction plate and is then reflected off the mirror facet, the correction plate adjusting a beam characteristic for each mirror facet or portion of a mirror facet. In another embodiment, alone or combined with the previous system, the light beam is routed along different paths to the mirror facets, for example (1) along a path parallel to the rotational axis of the facet wheel when directed onto a first mirror facet and (2) along a path perpendicular to the rotational axis when being directed onto a second mirror facet thereby adjusting scan angle while maximizing beam power.